Tuning indicator for frequency shift signals



April 1, 1953 L. L. LAKATOS 2,636,086

TUNING INDICATOR FOR FREQUENCY SHIFT SIGNALS Filed Dec. '26, 1951 -2 SHEETS--SHEET 1 t] gm r5 y WW5 I Pam/r6 m x E 6 If ZERO fix/5.

INVENTOR 17011 917. lallalai ATTORNEY the other for space.

Patented Apr. 21, 1953 TUNING INDICATOR FOR FREQUENCY SHIFT SIGNALS Louis L. Lakatos, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application December 26, 1951, Serial No. 263,265

14 Claims. 1

This invention relates to a tuning indicator for frequency shift telegraph signals, and more particularly to a cathode ray tube circuit for indicating the condition of tuning of a frequency shift telegraph receiver.

An object of this invention is to provide a simple cathode ray tube monitoring circuit for frequency shift telegraph receivers, in which no calibration or calibration adjustments are required.

Another object is to devise a novel null indicating device for indicating the tuning of frequency shift telegraph receivers, which device has zero output when the receiver is properly tuned.

A further object is to devise an indicating device for frequency shift telegraph receivers, in which no balancing of the mark and space inputs to the indicator is necessary.

Astill further object is to provide a novel type of coupling circuit for coupling the mark and space signals to a cathode ray tube tuning indicator for a frequency shift telegraph receiver, in which the indication produced on the cathode ray tube screen may be centered with respect to the tube face when the receiver is properly tuned,

without affecting the accuracy of the indication and without requiring any compensation by way of calibration.

Yet another object is to devise a novel amplifying circuit for coupling a balanced or doubleended input circuit to an unbalanced or singleended output circuit, while at the same time providing an amplifier input of high impedance such as to not unduly load a preceding stage.

An additional object is to devise a monitoring circuit for frequency shift receivers which indicates the degree of noise and interference present in the receiving channel.

In frequency shift telegraph transmission, two discrete frequencies are used, one for mark and The signal, when keyed by the normal telegraph waveform of substantially rectangular shape, alternates between these two frequencies in accordance with the keying. In

the usual receiver, the signal is amplified, con-,

verted to intermediate frequency which is amplified, limited and supplied to a frequency disson narrow band receivers can be used for improved signal-to-noise ratio. This places stringent requirements on the accuracy of receiver tuning, since the signal supplied to the discriminator (and which is derived from the receiver) should be centered on the discriminator characteristic for proper operation. Stated in other words, the mean between the mark and space frequencies supplied to the discriminator should be equal to the center frequency of the discriminator, so that the direct currents of opposite polarities out of the discriminator have the same absolute magnitude. In View of these stringent tuning requirements, it is quite desirable to have available a continuous indication of the condition of tuning, and according to this invention such an indication is provided.

In accordance with the invention, frequency shifted mark-space telegraph signals from a receiver are applied to the input of a discriminator. The output from the discriminator is applied in parallel to two diodes connected back-to-back and the other electrode of each of these diodes is connected to a respective one of the vertical deflecting plates of a cathode ray tube. This results in the production of a pair of dots on the cathode ray tube screen if the receiver feeding the discriminator is not tuned to the center of current is used to operate tone keyers or automatic recording apparatus. The usual difference between the two frequencies isof the order of 850 cycles or less in the communication bands between two and thirty megacycles for which reathe discriminator characteristic. A portion of the output of a tone keyer is applied to the horizontal deflecting plates in order to sweep out one of the dots, thus providing an indication of the sense of detuning. Alternatively, a modified sweep arrangement is caused to sweep a certain one of the dots to the right and the other to the left, to indicate the sense of detuning'. An A. C.-coupled amplifier may be used between the diodes and the vertical deflecting plates if amplification is required.

The foregoing and other objects of the invention will be best understood from the following description of some exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a schematic representation of one embodiment of the invention;

Figs. 2a-2e are various waveforms and. patterns illustrating the mode of operation of the embodiment of Fig. 1;

Fig. 3 is a diagrammatic representation of a modification of Fig. 1; r

Fig. 4 is a schematic representation of a modification of Fig. 1; and

Figs. 5a and 5b are trace patterns illustrating the operation of the Fig. 4 circuit.

Referring to Fig. 1, the transmitted frequency The windings 3 and 3 are differentially coupled.

to detectors 4 and 4' which comprise two diode structures either in separate envelopes or in a common envelope. The diode structures have their cathodes coupled together differentially by load. impedance-and--condenser units '5 and 6 to constitute a discriminator whereinpotentials. are produced representing mark interval when the received signal is at marl; frequency and representing space interval when the received signal is at space frequency. In the embodimentbeing described, the potential" at thec'athode'oi diode t varies from positive to'negative' directcurrent symmetrically about zero or ground" potential when the receiver is properly tuned to the center of the discriminator characteristicy'the cath-- ode of diode s beinggrounded. 'Positivediscriminator output may correspond to-received marl: frequency and negative'outp'ut-to" space frequency, or vice 'versayd'epending upon' the connections. tuned the positive and negative potentialvari'ations at the cathode. of diode 4 are'uneqii'ahas will appear more clearlyihereinafter. The disoriminator utilized may, for example, be'si'milar' to the discriminator-detector described in'Schocl: et al. Patent #2,515,668,:datedJuly 18, 1950.

The direct currentsoutput'(keyed) of the dis criminator described issuppliedto two diode structures '1 and 8' connected-'baclr-to back-and the associated respective load resistors 9 and Ii). More particularly, the .outputof the discriminator appearsbetween point A (connected to the cathode of diode t) and ground (the cathode of diode 3"). The anode of diode l is connected to point A and resistor 9' is connected between the cathode of this diode. and ground'ywhile the cathode of diode 3 is connected to'point Aand resistor in is connected between the'anode of this diode and ground. Diodes l and sare'p'referably two separate diode structures in a com mon' envelope. Due to the above connections, diode i conducts when A is positive with respect to ground and diode ii conducts when A is'negative with respect toground. .The cathode of diode '5 (point. B).is.conn'ected to one vertical deflecting plate H of a cathode ray oscilloscope tube it, while the anode ofdiode 8 (pointC) is connected to the other-(opposite) vertical defiectingplate l3of tube E2.

The. various electrodes of. cathode. ray tube I2 are energized by. suitable potentials as illus trated, producing an electron beam which is projectedtoward the faceorscreen. of the tube. This electron beam is subject. to deflection in the vertical direction. in. response to voltages-applied between deflecting plates Hand !3.

When a keyed frequency shifted. .telegraph signal is being. received, point. A is alternatively positive or negative with respect to ground, depending on the keying, due: to the. action. of the discriminator. If the signalinput frequencyto the discriminator iscentered. on the discriminator characteristicgthe; positive...and negativeexcursions. are equal, while if said signal input frequency is detuned from such center frequ n y.

When the receiver is improperly 1 the positive excursion becomes larger than the negative, or vice versa, depending on the sense or direction of detuning.

On the positive excursions of point A, diode l conducts and point B is positive with respect to ground, while diode 8 is non co'nducting and therefore point C is at substantially ground potential and would be at ground potential except for the contact potential of this diode. Consequently, upper deflecting plate I i is positive with "-"respect to lower deflecting plate 53 and the eiectron beam in tube 12 is deflected upward by an danrount 'proportionai 'to the potential difference betweenthe"twopiates, which in turn is pro portional to th'e'amplitude of the positive excur- 1 sionsotntherkeyed wave out of the discriminator.

On the negative excursions of point A, diode d'condu'cts and point C is negative with respect to ground, while diode l is non-conducting and therefore point B is: at substantially ground potential-.Jand would be at groundpotential except for the contact potential of this-diode. As a result, loweriplate I'd isnegative with respect to upper plate ii and the electronbeam in tube i2 is againdeflected upward'by an: amount proportional to the potential difierence between the two plates, which iii-turn isproportional to the amplitude of. the negative: excursions .of the keyed wave out of the discriminator.

Thus,- when the positive and negative excursions of the discriminator: output'waveare equal, the same upward:defiectionv ofzthe electron beam is produced by both the positive and negative swings, while if the two excursions of such output wave-tare unequal the two. upward deflections of the electron beam are" different.

Fig. 2a representsthe :keyed direct current output of the discriminator for a detuned or 'oii-tuned condition of'the receiver, the sense of .by X in Fig. 2c) is a measure of the amount of receiver detuning, but not the sense.

or course, i'f-the receiver-tuning were proper (in other words, if'there were: no detuning) the positive and negative excursions inFig. 2c would be equal in amplitude, in Fig. 2b the positive maximum voltage of point B would be equal in absolute value to the "negative maximum voltage of point C,*while in-Fig. 2cthe deflection of the electron beam would be represented by a straight horizontalline, indicating" equal deflections for both positive and negative voltage excursions of the discriminator output.

In the absence of'horizontal deflection of the electron beam, the trace on the cathode ray tube screen forthe detuned condition of Figs. 2a-2c. would "bezas. illustrated". inFig. 2d, consisting of two bright dots" with a faint Vertical line connecting them. When thetrace'pattern consists of two bright dots, rather than only one (as a result of unequalivertical'deflections for the two discriminator output polarities) the operator knows a detuned condition exist and also knows the amount. orthe detuning, butnot its sense. If the. tuning wereproperKthat is, no detuning of the receiver). thetwo dots would coincide to prod e in e e t on y a s n One method of obtaining an indication of the sene of detuning is to use the keyed tone output of a keyer unit for horizontal deflection of the electron beam, as illustrated in Fig. 1. A potentiometric resistor I4 is connected across the output of the discriminator and a portion of the voltage across such resistor is fed to a keyer unit l5. This keyer unit may include the following circuits in succession: one or more audio frequency amplifiers, a trigger driver, a double or two-stage trigger, and finally a tone keyer. The arrangement of the trigger driver and double trigger may, for exampIe, be like that disclosed in the aforementioned Schock et al. patent. The tone keyer is controlled by the final stage of the two-stage trigger and functions to provide keyed (on-off) tone output, providing tone output on one of the polarities of the discriminator output (corresponding to either mark or space) and no output or zero output on the other. The keyed tone output appears across a transformer secondary winding 16 and is applied between the horizontal deflecting plates I! and N3 of cathode ray tube l2. One end of winding it is grounded, as is one deflecting plate It, while the other end of winding it is connected directly to deflecting plate IT.

The tone output produced by the tone keyer is of course alternating current, and appears across deflecting plates II and I8 simultaneously with the appearance at plates H and 13 of either one discriminator-derived deflecting voltage or the other, but not both. Consequently, one or the other of the dots in Fig. 2d is swept out to a horizontal line, producing the trace pattern illustrated in Fig. 2e. In this way, by knowing beforehand the relation between the tone keyer output and the positive and negative excursions of the discriminator output (corresponding to mark and space signals), the sense of detuning may be determined from the pattern of Fig. 2e, since only the particular dot representing a certain polarity is swept out. In other words, the polarities represented by the two dots in Fig. 2d are identified, and the sense of detuning is indicated. The transitions between mark and space are represented by the slanting lines in Fig. 2e, these slanting lines being in random positions in the absence of synchronism between the keying frequency and the horizontal deflection frequency (the frequency of the tone).

Usually, the setup is such that mark signal is represented by a lower frequency input to the discriminator than is space signal, and the tone keyer operates to produce a tone output for mark signal and no tone for space signal. Thus, the dot representing mark signal is swept out to produce a line.

If the receiver is detuned in a direction opposite to that illustrated inFig. 2a the negative excursions would exceed in amplitude the positive excursions, in Fig. 2b the negative maximum of point C would exceed in absolute value the positive maximum of point B and in Fig. 2c the deflection curve would be reversed or flipped over. In Fig. 2e the dot would be below the horizontal line, rather than above as shown.

In Fig. 2e, as the receiver tuning is changed in the proper direction the dot and the horizontal line trace approach each other and when the tuning is correct the dot and the linetrace coincide. Thus, on a centered signal both points B and C vary (in voltage) up and down together and there is no net vertical deflection of the cathode ray or electron beam.

Noise or interference appearing at the discriminator output is visible as random vertical deflec tions (commonly termed "hash) on one or both dots in Fig. 2d, or in Fig. 2e on the dot and/or the line trace. In this manner, a continuous automatic indication of the degree of noise and interference present in the receiving channel is provided.

The character of the keying transitions is made evident from the appearance of the slant line traces in Fig. 2e.

In the manner above described, a continuous indication is provided of the condition of receiver tuning, with respect to the discriminator characteristic. It will be noted that the indicator of 15 this invention is a null indicator, with zero output (zero net deflection, or coincidence of line trace and dot in Fig. 2e) at resonance or at proper tuning, and unequal deflections off resonance or when the receiver is detuned. No balancing, calibration, or adjustments are required.

In a practical case, amplification is usually required between points B and C and the vertical plates of tube I2. This could be A. C.-coupled in order to remove the D. C. component, represented by the distance in Fig. 20. When the D. C. component is removed 3 in this way and when no fluctuating signal is applied to the deflecting plates of the cathode ray tube, there will be no deflection of the electron beam, meaning that the spot-trace centers itself, up and down, on the screen of the tube. A practical circuit with A. C.-coupled amplification, which was built and successfully tested, is illus trated in Fig. 3.

In Fig. 3, the diode-resistor combinations 1, 9 and 8, II] are connected across the output of the discriminator (between a varying-potential lead and ground) in exactly the same manner as in Fig. 1. From point B (cathode of diode 7) a coupling extends through a coupling capacitor I9 to the grid of a triode structure 20 the anode of which has no load resistor but is connected through a resistor 2| of low value to the positive terminal of a source of unidirectional potential. The cathode of triode 20 is connected through two series-connected resistors 22 and 23 to ground, while the grid side of capacitor I9 is connected through a resistor 24 to the junction of resistors 22 and 23. From point C (anode of diode 8) a coupling extends through a coupling capacitor 25 and a resistor 26 to the grid of a triode structure 2! the anode of which is connected through a load resistor 28 to the junction of the anode of triode 20 and resistor 2!. The cathode of triode 27 is connected to the cathode of triode 20, so that these two cathodes utilize the same resistors 22 and 23 in common. The grid side of resistor 26 is connected through a resistor 29 to the junction of resistors 22 and 23. The resistors 26 and 29 consistute a voltage divider whereby only a portion of the voltage at point C is applied to the grid of triode 21. This voltage dividing network provides compensation for the contact potential of the two diodes I and 8 connected back-to-back. thus making the voltages at B and C (as they affect the deflecting plates I l and I 3.) more nearly ap proach zero when the respective diodes are not conducting.

The inputs of the triodes 20 and 2'! are balanced push-push, as may be seen from Fig. 21).

7 5 Whenpoint C is changing from its most nega-r aesaosc tive" SKCUISiOILtO'%Z8IO1thatI is; upwards (becoming morepositive).,'.point B is changing from substantially zero:to-its mostpositive excursion, that is; also upwards or more positive. In other words; the top of the :negative square wave of point 'C, corresponding substanti'allyto the zero axis or its most positive position (when-diode 8 is not conducting); occurs atthe same timethat diode I is conducting: and point B is-most positive. The average D. C. potentials-of :the two points are of course'of opposite polarity; point C being negative and point- B being positive. Output is taken trom acrossload'resistor 2% by means of a "coupling capacitor 30 one sideof which is conneotedto'the anode of'diod'e 2? and the other' side of which is connected'to one vertical'deflecting plate" I L the other deflecting plate It being grounded.Thus, the-output of triodes 2G and 21 is'unbalanced or single-ended. Amplifying triodes '2fland'Zl'thus constitute a balanced-input, unbalanced-output amplifier-between diodes 1- 'and il -and cathode ray' tube 62.

The-triode-Zflprovides a high impedance output xcircuit for -diode I; thus notu'nduly loading said diode. The triode 27 is an amplifier which is grid-driven by diode 8, thus presenting a high impedance output circuit for such diode. Triode 20 operates as a cathode follower stage which is grid-drivenpbydiode. l and which in'turn drives the cathode of triode 21, from-the anode of which to the diode by the cathode circuit of the triode;

hence; the'cathode follower stage 25! isutilized. with the'high input-.impedanceplow output impedance which ischaracteristic of cathodefollower stages.

The reason for-using avoltagedivider net-v work 26, 29 in the grid input circuit of triode ill, and for not using one in thegrid input circuit of. triode'20, should now be apparent. It is desirable to equalize 'theidriving voltages fed to the grid and-to the. cathode of triode 21. There 1 is a certain signal loss in the'cathode follower stage 20, so thatthere'would be a similar loss in the signal fed to thecathode of triode 21. To balance this loss, thez signal fed' to the grid of triode 2'! is'reduced by'the voltage dividing net work- 26, 29' and since the-cathode follower stage 20 is. already unavoidably lossyjthe full signal voltage is applied to itsigrid.

The output of amplifying stage 21 is fed to one vertical deflecting-plate ofthe cathode ray tube [2 through capacitor 30. The other vertical deflecting plate 13 of tube i2 is grounded. As in Fig. l. the output of a tone keyer is applied betweenthe horizontal'defiecting plates I! and i8, plate [8 being grounded.

In operation, the voltage on the discriminator output lead connected to the anode of diode i and to'the cathode of diode 8 becomes alternatively positive andnegative with respect to ground in accordance with the keyingas in Fig. 1. When this lead is positive, point B ispositive and point C is at ground potential. The positive-going potential at B is appliedto the grid of triode 20 and produces a positive voltage at itscathode which iszapplied' to the' cathode of triodil. This produces" the same efi'ect :as a negative voltage-applied" to the grid of this triode. sothatztheplate current" intriode 2T is reduced, giving a'ipositive voltage at its anode which is appliedtodefiecting plate H to deflect-the electron .beam'upwardg'defleeting plate .13 being connected to ground. Whenthe'ungrounded discriminator lead isznegative, point C. is negative. and point B. is, atground potential. .The negative goingpotential atG is applied to the: grid of triode'l' and-reduces the platecurrent inthis tube; Thus, a positive volt age again appears at the anode of triodetfil which again deflects. the electron bcamin. tube !2 upward; through thezapplication of thispositive voltage'to deflecting-plate H. Since. the. .tone lzeyer. output. is used for: horizontal sweep in Fig. 3! also, the pattern produced oirthe cathode ray tube: screen'by the 3 circuit is. exactly: similar to that previously. described Ln-connection with Fig. 1; the pattern for a particular direction of receiver mistuning being represented: 26.

Due to'the' fact that capacitors i9, and- 3B are-used in the'Fig. S circuit, the amplifier'is A. C.-coupled, removing the D. C. ccunponent represented bythe distance in Fig. 2c. The spot-traceon the screen of the cathode ray tube thus centers itself, upand down. when loo-fluctuating signal is applied to -thedefleeting plates of thetube.

In an embodiment according to Fig. 3 which was built and successfully tested, the following component values were used. Itv is tobe understood. thatthesevalues. are given merelyby way ofillustration andnot by way of limitation.

Tube '1 "6AL5 Tube 8 '6AL5 Tube" 8 2 2BP1 Tube-{2d ".L2AX'7 Tube'z'i 12AX7 Resistor .i ohms 5601.000 Resistor id do 560,000 Resistor 2i do "10,000 Resistor 22 do LOGO Resistor 23 do 39,090 Resistcrid lmegohms 1.2 Resistor Z6 ohms 5101000 Resistor 28 "don" 270,080 Resistor 29 do 680,060 (lapacitorlii rnfd w 0.1 Capacitor 25 mfd 0.1 Capacitor 3t mfd 0.1

It should be understood that the balanced-tounbalanced amplifier of Fig. 3 will operate equally well when the two input voltages thereto are either in-phase or out-or-phase. If they are inphase (push-pushas described) the net output, for equalinputs, is'zero, as previously described, while if they are out-o f-phase (push-pull) the two currents due to the grid drive and to the cathode drive of tube 27 would add in this tube.

It will be recalled that in Figs. 1 and 3, the output of a tone'keyer is applied to the horizontal deflecting plates, to provide an indication of the sense of detuning or mistuning of the receiver. Other methods for providing sense indication are possible, and one such method is illustrated in Fig. 4. IiiFig. 4, the diodes T and 8 and load resistors 9 and ill are coupled to the discriminator output in exactly the same manner as inFig. 1, point B (cathode of diode Wibeing connected to vertical deflecting plate I land point C(anode of diode 8) being connected to vertical deflecting plate l3. A portion of the discriminator output, which consists of a keyed direct current square wave extending above and below the zero aXis of potential, as illustrated in Fig. 2a, is applied to a low pass filter 3|, which passes the keying frequency. The output of filter 3i is applied to a trigger circuit 32, which may be a two-stage trigger circuit quite similar to the double-trigger keyer control circuit disclosed in Schock et a1. Patent #2515668, dated July 18, 1950. The output of trigger circuit 32 is applied to a differentiating circuit 33, which may be an ordinary RC- type differentiating circuit.

The filter 3| functions somewhat as an integrating circuit and attenuates high frequency components, so that if the output of this filter were fed directly to the differentiating circuit, this latter circuit would not have a steep wavefront applied to it; in this case the output of circuit 33 would be low, and lacking in the high frequency components required for a narrow pulse. The function of trigger circuit 32 is to restore the steep wavefront of the square wave applied to the input of filter 3! at the output of circuit 32. The differentiation of this steep wavefront square wave by circuit 33 results in narrow pulses at its output.

The narrow-pulse output of circuit 33 is applied between horizontal deflecting plates I? and it of cathode ray tube l2, to provide a sweep voltage. Diflerentiating circuit 32 operates to differentiate the voltage applied to its input, as previously described. Thus, the upward-going portion of the square wave illustrated in Fig. 2a results in the production of a positive pulse between the high side of the output of circuit 33 and ground, which positive pulse is applied to horizontal deflecting plate ll (horizontal deflecting plate It being grounded); similarly, the downwardegoing portion of the Fig. 2a square wave results in a negative pulse being applied between plate I! and ground. When horizontal deflecting plate I! is positive with respect to plate [8 (ground) the deflection of the electron beam will be to the left, while when plate ll is negative with respect to plate E8 the deflection of the electron beam will be to the right.

The square wave applied to circuit 32, and differentiated thereby, is delayed a few milliseconds, with respect to the square wave variations of points B and C applied to the vertical deflecting plates l l and l 3, because of the low pass filter 3 I. This allows the vertical deflections of the beam corresponding to the two respective portions of the discriminator output wave (represented by the two dots of Fig. 2d, for a certain condition of receiver detuning) to be effected before the spots are swept out horizontally. Since the positive and negative voltage output pulses are produced by circuit 32 in response to the mark-space transitions of the square wave discriminator output, a few milliseconds after such transitions, and since a positive voltage output pulse corresponds to the marking signal and a negative voltage output pulse to the spacing signal, or vice versa, the mark dotof Fig. 2d is traced out to the right and the space dot to the left, or vice versa, depending upon the connections, in substantial synchronism with the vertical deflection. Thus, for one particular sense of receiver detuning the trace pat tern on the screen of tube [2 will be somewhat as illustrated in Fig. a, which shows one dot swept out to the left and the other to the right, ofa central position. If the receiver is detuned in theopposite direction or opposite sense, the pattern of Fig. 5a will be reversed, that is, the dot swept out to the right will be below, rather than above, the dot swept out to the left. Since for any particular setup the mark dot is swept out in one particular direction and the space dot in the other direction, the sense of detuning of the receiver will be indicated.

If the tuning of the receiver is proper, the trace pattern produced will be about as illustrated in Fig. 5b, with the two dots coinciding (as explained above in connection with Fig. 2d) and one being swept out to the left and the other to the right. This provides a line trace with a dot in the center thereof, see Fig. 5b.

What is claimed is:

1. A tuning indicator for a frequency shift telegraph receiver comprising in combination, frequency discriminator means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the opposite polarity for space frequency, the relative magnitudes of said two peaks representing the condition of tuning of said recevier, a cathode ray tube having means for producing an electron beam and means for deflecting said beam, and means for applying said wave to said deflecting means to produce two separate deflections of said beam, one corresponding to the amplitude of one peak of said wave and the other corresponding to the amplitude of the other peak of said wave.

2. An indicator in accordance with claim 1, including additional deflecting means operatively coupled to the tube for causing the two produced deflections to have different visual aspects.

3. An indicator in accordance with claim 1, wherein the two deflections produced are both in the same direction with respect to a reference point on the fluorescent screen of the tube, said indicator including additional deflecting means operatively coupled to the tube for causing the r two produced deflections to have difierent visual aspects.

4. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the opposite polarity for space frequency, means feeding said Wave to a pair of parallel circuits each consisting of a unilaterally-conducting device and an output impedance in series, the devices in said two circuits being oppositely disposed, a cathode ray tube having means for producing an electron beam and means for deflecting said beam, and means for applying the voltages developed across each of said impedances to said deflecting means to produce two separate deflections of said beam each one of which corresponds to the amplitude of a respective one of said developed voltages.

5. An indicator in accordance with claim 5, including additional deflecting means operatively coupled to the tube for causing the two produced deflections to have different visual aspects.

6. An indicator in accordance with claim 4, wherein the two deflections produced are both in the same direction with respect to a reference point on the fluorescent screen of the tube, said indicator including additional deflecting means 1 1 operatively coupled to the-tube for causing the two produced deflections to have different visual aspects.

7. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of t the opposite polarity for space frequency, a tone keyer receptive of said wave for producing on-off keyed tone keyed inaccordance with said wave, a cathode ray tube having means for producing an electron beam and two separate means for deflecting said beam in different directions, means for applying the output of said tone keyer to one of said deflecting means, andmeans for applying said wave to the other of said deflecting means to produce two separate deflections of said beam, one corresponding to the amplitude of one peak of said wave and the other corresponding to the amplitude of the other peak of said wave.

8. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the'opposite polarity for space frequency, means for differentiating said wave to produce pulses of opposite polarities corresponding to successive transition points of said Wave, a cathode ray tube having means for producing an electron beam and, two separate means for deflecting said beam in different directions, means for applying the outputlof said differentiating means to one of said deflecting means, and means for applying said, wave to the other of said deflecting means to produce two separate deflections of said beam, one corresponding to the amplitude of one peak of said wave and the other corresponding to the amplitude of the other peak of said wave.

9. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the. frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the opposite polarity for space frequency, means feeding said waveto a pair of parallel circuits eachconsisting of a unilaterally conducting device and an output impedance in series, the devices in said two circuits being oppositely disposed, a tone keyer receptive of said wave for producing an on off keyedtone keyed in accordance with said wave, a cathode ray tube having means for producing an electron beam and two separate means for deflecting said beam in different directions, means for applying the output of said tone keyer to one of said deflecting means, and means for applying the voltages developed across each of said impedances to the other of said deflecting means to produce two separate deflections of said beam each one of which corresponds to the amplitude of a respective one of said developed voltages.

10. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency, shifted signals a keyed direct current wave of substantiallysquare waveform having a peak of one polarity with respect to a fixed reference potential iormark frequency and having a peak of the opposite polarity for space frequency, means feeding said wave to a pair of parallel circuits each consisting of a unilaterally-conducting de vice and an output impedance in-series, the de vices in said two circuits being oppositely dis posed, means for differentiating said wave to produce pulses of opposite polarities corresponding to successive transition points of said wave, a cathode ray tube having means forproducingan electron beam and two separate means fordeflecting said beam in different directions; means for applying the output of said differe'n tiating means to one of said deflecting means; and means for applying the voltages developed across each of said imped'ances to the other or said deflecting means to produce two separate deflections of said beam each one of which corresponds to the amplitude of'a respective one of said developed voltages.

11. A tuning indicator for a frequency-shift telegraph receiver comprising in combination; means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak'of one polarity with respect to a fixed reference po tential for mark frequency and having a peak of the opposite polarity for space frequency, a cathode ray tube having means for producing. an electron beam and means for deflecting said beam, and means for applying said wave to said deflecting means to produce two separate deflections of said beam, one "corresponding to the amplitude of one peak of said wave and the other corresponding to the amplitude of the other peak of said wave; said means for applying includingthe control electrodes of the respective devices,

means connecting the two electron-emitting elec-' trodes together and to a common impedance, and an output circuit including said deflecting means connected to the electron-receiving electrode of said second device.

12. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals -a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark fre uency and having a pear: of the opposite polarity for space fre uenc means feeding said wave to a pair of parallel ci'rcuitsea'ch consisting of a unilaterally-conducting device and an, output impedance in series, devices in said two circuits being oppositely dis-i posed, a cathode ray tube having means for producing an electron beam and means for deflecting said beam, and means for applying the voltages developed across each of'said impedances to said deflecting means to produce two separate defied tions of said beam each oneof which corresponds to the amplitude of a respective one of said deplying input voltages'of like'phase, derived from across said impedances, to thecontrol electrodes of the respective devices, means connecting the two electron-emitting electrodes together and to a common impedance, and an output circuit including said deflecting means connected to the electron-receiving electrode of said second device.

13. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the opposite polarity for space frequency, means feeding said wave to a pair of parallel circuits each consisting of a unilaterally-conducting device and an output impedance in series, the devices in said two circuits being oppositely disposed, a cathode ray tube having means for producing an electron beam and means for deflecting said beam, and means for applying the voltages developed across each of said impedances to said deflecting means to produce two separate deflections of said beam each one of which corresponds to the amplitude of a respective one of said developed voltages; said means for applying including a first triode electron discharge device having anode, cathode and control electrodes, a second triode electron discharge device having anode, cathode and control electrodes, means for supplying input voltages of like phase, derived from across said impedances, to the control electrodes of the respective devices, means connecting the first device as a cathode follower stage driving the second device, and an output circuit including said deflecting means connected to the anode electrode of said second device.

14. A tuning indicator for a frequency shift telegraph receiver comprising in combination, means for deriving from the received frequency shifted signals a keyed direct current wave of substantially square waveform having a peak of one polarity with respect to a fixed reference potential for mark frequency and having a peak of the opposite polarity for space frequency, means feeding said wave to a pair of parallel circuits each consisting of a unilaterally-conducting device and an output impedance in series, the devices in said two circuits being oppositely disposed, a tone keyer receptive of said wave for producing on-ofi keyed tone keyed in accordance with said wave, a cathode ray tube having means for producing an electron beam and two separate means for deflecting said beam in different directions, means for applying the output of said tone keyer to one of said deflecting means, and means for applying the voltages developed across each of said impedances to the other of said deflecting means to produce two separate deflections of said beam each one of which corresponds to the amplitude of a respective one of said developed voltages; said means for applying including a first triode electron discharge device having anode, cathode and control electrodes, a second triode electron discharge device having anode, cathode and control electrodes, means for supplying input voltages of like phase, derived from across said impedances, to the control electrodes of the respective devices, means connecting the first device as a cathode follower stage driving the second device, and an output circuit including said other deflecting means connected to the anode electrode of said second device.

LOUIS L. LAKATOS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,154,379 Estes Apr. 11, 1939 2,178,074 Jakel et a1 Oct. 31, 1939 2,553,674 Purington May 22, 1951 2,613,271 Trevor Oct. 7, 1952 

